Evidence record / codex
A dated record of one change, kept so the writing that cites it can be checked. Compiled from the sources listed below by the research run, not written for reading. The judgment lives in the signals and issues that cite it, below.
2026-09-21-codex-default-model-moved-to-gpt-6-astra-in-the-0-153-x-hotfix-train-not-in-a-minor
Default model moved to GPT-6-Astra in the 0.153.x hotfix train, not in a minor. When model is unset, a patch release changed which model runs. 0.153.2 says the Astra Fast tier is “2x speed, increased usage”. 0.154.0 says fresh sessions and forks now “respect server model defaults unless explicitly overridden” (#43177), so the effective default can also come from the server catalog. 0.154.0 updates the bundled OpenAI Docs skill with Astra migration guidance (#42931). Changelog (docs-only): GPT-5.3-Codex-Spark was deprecated 2026-09-14. GPT-5.5 retires from Codex with ChatGPT sign-in on 2026-10-14, and the changelog says to switch to gpt-5.6-sol. Marketing for the “GPT-6 Astra” launch is out of scope. The Codex primary surfaces record only the catalog, picker, and default change above.
Channel: tagged-release. Half: both. Date: 2026-09-03 (config-only) -> 2026-09-04 (bundled default).
Operator consequence: Any fleet that leaves model unset changed model on a patch upgrade (0.153.3 -> 0.153.4). Pin model explicitly if cost, latency, or eval baselines matter. Re-run evals if you did not pin. Grep configs, custom agents, and scheduled tasks for gpt-5.5 and gpt-5.3-codex-spark before 2026-10-14.
Receipt
Finding metadata
Run: 2026-09-21-weekly-digest-2026-08-20_2026-09-21-frontier-v0
Finding ID: 2026-09-21-codex-default-model-moved-to-gpt-6-astra-in-the-0-153-x-hotfix-train-not-in-a-minor
Accepted signals
Profile citations
- Codex / claim / default-model-hotfix
Source links
Primary links, including exact changelog lines when available.
Versioned source: run artifact